Apparatus in which both recording of and optical reading of information with high recording density can be performed, and their technique is known. As methods of recording information on optical recording media, there are two kinds of methods. In one method, pits corresponding to bits are formed by applying radiant energy to a recording media. In the other method, domains with different optical characteristics, such as reflection factor, absorption coefficient, refractive index are formed corresponding to bits by applying radiant energy to a recording media.
In the former, radiant energy causes thin films, such as metal on a base, to partially melt or vaporize, so that pits are formed in the recording media. In the latter, radiant energy causes the phase transition of a thin film on a base, or radiant energy causes a change of bonding between atoms so that domains with different optical characteristics are formed. This invention relates to the latter method.
Optical recording media in which recording can be performed by a change of optical characteristic generally should have the following characteristics:
(i) High-speed recording can be performed with a small amount of energy for recording,
(ii) Recording with high recording density can be performed,
(iii) Optical contrast of recorded parts to unrecorded parts is large,
(iv) Rewriting can be performed,
(v) Media material is a stability allowing both long-time preservation and long use possible, and
(vi) The media material is not toxic or dangerous.
Optical recording media which are known to this date are as follows.
(i) Thin films which consists of low melting point metal, such as Te, Se, or of an alloy of the said low melting point metals,
(ii) Thin films which consists of a metallic compound, such as TeOx,
(iii) Organic thin films which consist of dyes, such as fluorecein, cyanine, or pigment, and
(iv) Thin films which consist of photochromic compounds.
As to organic media, many kinds of materials such as the heat-mode type or media material of the photon-mode type are proposed. However, they have disadvantages, for example: Sensitivity is insufficient, contrast of the recorded part to the unrecorded part is small, and it is difficult to make the S/N (signal to noise) ratio higher, further, the stability after recording is insufficient.
Therefore, they are practically unsatisfactory. On the other hand, as to inorganic media, many kinds of materials are proposed. One practice was to provide a light disc memory of the additional record type (DRAW type) which is made by Te system compounds, such as Te-C and TeOx. Further, recently, research has been made actively into light disc memory of the rewriting type (E-DRAW type), for example, in light disc memories in which the phase transition between crystal and non-crystal TeOx is utilized for recording.
However, when the phase transition between crystal and non-crystal TeOx is utilized for recording, the reflection factor of the unrecorded part is about 15% to 20%, while that of the recorded part is about 30% to 40%. The difference between both is about 15% to 20%, which is insufficient. Further, when the phase transition is utilized for recording, there is a limit to making the recording speed higher. Furthermore, Te system media have a problem that makes it desirable to lower the toxicity of said media or to detoxicate it.
It is strongly desired to develop recording media in which the characteristics (i) to (v) as stated above are improved, to make the capacity higher, and to decrease error ratio by making the S/N ratio higher on a full scale.
Accordingly, it is an object of the present invention to provide an organic optical recording media in which bits are formed at high speed and with high recording density, and with large optical contrast of the recorded part to the unrecorded part.
In this invention, the word "optical recording" signifies both recording with radiant energy rays and reading optically recorded information. Therefore, the word "optical recording media" signifies media in which information is recorded in such manner that optical reading can be performed.
The recording media according to this invention has the following advantages:
(i) High-speed recording can be performed in a period of less than 10 nsec,
(ii) Recording can be performed with low energy of less than about 80 mJ/cm.sup.2,
(iii) Recording can be performed with high recording density greater than 10.sup.8 bits/cm.sup.2, either in the binary system or in the n-system,
(iv) Optical contrast of the recorded part to the unrecorded part is large, so that the error ratio can be lowered advantageously, and
(v) Recording media has no toxicity.